The present invention relates to a polishing agent and a polishing method for polishing the surface of an insulating film or a coating insulating film constituting a semiconductor integrated circuit or an optical glass element.
When a semiconductor integrated circuit is manufactured with a wiring substrate of silicon, a variety of insulating films are used and their surfaces need to be machined into predetermined shapes. Polishing has been widely used as an effective technique for planarizing or smoothing the surfaces of the insulating films. Especially in the machining of a semiconductor integrated circuit, the chemical mechanical polishing (hereinafter referred to as the “CMP”) has been examined for planarizing the surfaces. In Proceedings VLSI Multilevel Interconnection Conference, pp. 20–26, 1991, for example, there is disclosed a method for polishing and planarizing an SiO2 film using a polishing agent (hereinafter referred to as the “silica slurry”) prepared by dispersing fine SiO2 particles (colloidal silica or fumed silica) in an aqueous solution of potassium hydroxide (KOH). It is well known that the addition of the chemical reaction effect accelerates the polishing rate (hereinafter referred to as “removal rate”) by keeping the liquid alkaline in a region where the pH value is higher than 7. However, the neutral region actually varies within a pH range of 6.5 to 7.5. Therefore, the solution is actually stable as an alkali in the pH region over 7.5 and as an acid in the pH region below 6.5.
When an insulating substance such as of a glass substrate other than a thin film used for manufacturing a lens and a liquid crystal display element, especially, a substance composed mainly of SiO2 is polished, there is a known polishing agent (hereinafter referred to as the “ceria slurry”) using cerium oxide powder. This ceria slurry is explained, for example, in Kikai no Kenkyu, volume 39, No. 12, pp. 1296–1300, 1987, and Erekutoronikusuyo kessyozairyonoseimitukakogijutu, pp. 251–256, Saiensu Foramu Co., Tokyo, 1985. The actual polishing is effected by mixing cerium oxide powder in water. In the prior art polishing method using the ceria slurry, a mixture of the cerium oxide powder and water is merely used as the polishing agent. In short, the ceria slurry is not expected to exhibit a chemical effect using acidity or alkalinity but is used to bring about the so-called “mechanical polishing effect.”
The ceria slurry can be applied to optical glass elements or the like but will degrade the characteristics of a semiconductor integrated circuit if applied to the process of manufacturing a semiconductor integrated circuit. If the insulating film on a bipolar transistor, for example, is polished by the ceria slurry and is subjected to a heat treatment essential for the semiconductor manufacturing process, the current amplification factor hfc of the bipolar transistor markedly lowered. If, moreover, the insulating film on a diode is polished by using the ceria slurry, there arises a problem that the rectifying characteristics of the diode deteriorate.